Fix some zephyr build issues

[erlingrj]

1. The user-provided prj.conf was not included.
2. We generated CMake code that linked against some Zephyr kernel library this generated a cyclic-dependency. I am trying to remove this linkage and lets see if all the tests still pass

[erlingrj]

Unfortunately, I am not able to find a good solution to this. It is strangely complicated to just link the following three things without creating a CMake target cycle or other linker issues:

1. Reactor-c library
2. LF application
3. Zephyr kernel

Im afraid I will have to come back to this in March

[erlingrj]

I am updating this PR to just fix a tiny mistake in the code-generated CMakeLists for Zephyr. Now we check for any prj.conf file in the src-gen directory and includes it. This is used by our custom west command.

[erlingrj]

@lhstrh, all tests pass except the label-test which doesn't pass when I re-run it, even though there now is a label. We don't need to rerun the entire test suite to get it all green I think...

[lhstrh]

The reason for the test failure is clear from the output:

Error: Label error. Requires at least 1 of: feature, enhancement, fix, bug, bugfix, cleanup, refactoring, documentation, docs, test, tests, testing, upgrade, bump, dependency, version, misc, miscellaneous, ignore, exclude, trivial, duplicate, question, invalid, wontfix, ci, automated, experimental. Found: zephyr

I added the label bugfix.

[lhstrh]

👍